The intent of the project is to understand the mechanisms by which vertebrates perceive earth's magnetic field and skylight polarization patterns. Detection of both cues has been demonstrated in a diversity of higher animals including mammals, suggesting that the relevant sensory systems may be virtually ubiquitous. Nevertheless, we know very little about how these sensory inputs are transduced and of what value they are to the organisms. Our methodology involves a comparative approach using a very sensitive assay--orientation behavior--with vertebrate species known to have well-developed sensitivity to earth-strength magnetic fields and skylight polarization cues. The object is to develop model systems with which it will be possible to determine the functional properties and adaptiveness of the receptor systems. We will use already-developed experimental and analytical techniques, depending primarily upon laboratory tests under carefully-controlled conditions but also specific field tests under natural conditions. Our findings will not only contribute to an understanding of the importance of polarized light and magnetic field sensitivity in animal orientation behavior, but will help in understanding the physical limitations and adaptive functions that have shaped the sensory repertoires of higher vertebrates, including humans. In addition, a better understanding of magnetic field sensitivity in other vertebrates will aid in critically evaluating the recent controversial claim of an unconscious magnetic sense in humans. Finally, recent evidence has demonstrated the association of both polarized light and magnetic field sensitivity, as well as control of periodic (daily/seasonal) behaviors, with the pineal complex of the brain. Our findings will help to evaluate the possibility that this complex is fundamentally involved in the integration of spatial and temporal phenomena and, in turn, will contribute to a better understanding of the changes that have occurred in the functioning of the pineal complex in different vertebrate groups.